Neuroscientists create images of Ghostly Aberration in subjects

Posted on November 8, 2014

Ghosts exist only in the mind, and scientists know just where to find them, an EPFL study suggests. Patients suffering from neurological or psychiatric conditions have often reported feeling a strange "presence". Now, EPFL researchers in Switzerland have succeeded in recreating this so-called ghost illusion in the laboratory.

On June 29, 1970, mountaineer Reinhold Messner had an unusual experience. Recounting his descent down the virgin summit of Nanga Parbat with his brother, freezing, exhausted, and oxygen-starved in the vast barren landscape, he recalls, "Suddenly there was a third climber with us... a little to my right, a few steps behind me, just outside my field of vision."

It was invisible, but there. Stories like this have been reported countless times by mountaineers, explorers, and survivors, as well as by people who have been widowed, but also by patients suffering from neurological or psychiatric disorders. They commonly describe a presence that is felt but unseen, akin to a guardian angel or a demon. Inexplicable, illusory, and persistent.

Olaf Blanke's research team at EPFL has now unveiled this ghost. The team was able to recreate the illusion of a similar presence in the laboratory and provide a simple explanation. They showed that the "feeling of a presence" actually results from an alteration of sensorimotor brain signals, which are involved in generating self-awareness by integrating information from our movements and our body's position in space.

In their experiment, Blanke's team interfered with the sensorimotor input of participants in such a way that their brains no longer identified such signals as belonging to their own body, but instead interpreted them as those of someone else. The work is published in Current Biology.

The researchers first analyzed the brains of 12 patients with neurological disorders - mostly epilepsy - who have experienced this kind of "apparition." MRI analysis of the patients's brains revealed interference with three cortical regions: the insular cortex, parietal-frontal cortex, and the temporo-parietal cortex. These three areas are involved in self-awareness, movement, and the sense of position in space (proprioception). Together, they contribute to multisensory signal processing, which is important for the perception of one's own body.

The scientists then carried out a "dissonance" experiment in which blindfolded participants performed movements with their hand in front of their body. Behind them, a robotic device reproduced their movements, touching them on the back in real time. The result was a kind of spatial discrepancy, but because of the synchronized movement of the robot, the participant's brain was able to adapt and correct for it.

Next, the neuroscientists introduced a temporal delay between the participant's movement and the robot's touch. Under these asynchronous conditions, distorting temporal and spatial perception, the researchers were able to recreate the ghost illusion.